/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */


package apk.base;


import java.io.Serializable;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.RandomAccess;

import static apk.base.Preconditions.checkArgument;
import static apk.base.Preconditions.checkElementIndex;
import static apk.base.Preconditions.checkNotNull;
import static apk.base.Preconditions.checkPositionIndexes;


/**
 * Static utility methods pertaining to {@code byte} primitives, that are not already found in
 * either {@link Byte} or {@link Arrays}, <i>and interpret bytes as neither signed nor unsigned</i>.
 *
 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/PrimitivesExplained">primitive utilities</a>.
 *
 * @author Kevin Bourrillion
 * @since 1.0
 */
// TODO(kevinb): how to prevent warning on UnsignedBytes when building GWT
// javadoc?
public final class Bytes {
    private Bytes() {
    }

    /**
     * Returns a hash code for {@code value}; equal to the result of invoking {@code ((Byte)
     * value).hashCode()}.
     *
     * <p><b>Java 8 users:</b> use {@link Byte#hashCode(byte)} instead.
     *
     * @param value a primitive {@code byte} value
     * @return a hash code for the value
     */
    public static int hashCode(byte value) {
        return value;
    }

    /**
     * Returns {@code true} if {@code target} is present as an element anywhere in {@code array}.
     *
     * @param array  an array of {@code byte} values, possibly empty
     * @param target a primitive {@code byte} value
     * @return {@code true} if {@code array[i] == target} for some value of {@code i}
     */
    public static boolean contains(byte[] array, byte target) {
        for (byte value : array) {
            if (value == target) {
                return true;
            }
        }
        return false;
    }

    /**
     * Returns the index of the first appearance of the value {@code target} in {@code array}.
     *
     * @param array  an array of {@code byte} values, possibly empty
     * @param target a primitive {@code byte} value
     * @return the least index {@code i} for which {@code array[i] == target}, or {@code -1} if no
     * such index exists.
     */
    public static int indexOf(byte[] array, byte target) {
        return indexOf(array, target, 0, array.length);
    }

    // TODO(kevinb): consider making this public
    private static int indexOf(byte[] array, byte target, int start, int end) {
        for (int i = start; i < end; i++) {
            if (array[i] == target) {
                return i;
            }
        }
        return -1;
    }

    /**
     * Returns the start position of the first occurrence of the specified {@code target} within
     * {@code array}, or {@code -1} if there is no such occurrence.
     *
     * <p>More formally, returns the lowest index {@code i} such that {@code Arrays.copyOfRange(array,
     * i, i + target.length)} contains exactly the same elements as {@code target}.
     *
     * @param array  the array to search for the sequence {@code target}
     * @param target the array to search for as a sub-sequence of {@code array}
     */
    public static int indexOf(byte[] array, byte[] target) {
        checkNotNull(array, "array");
        checkNotNull(target, "target");
        if (target.length == 0) {
            return 0;
        }

        outer:
        for (int i = 0; i < array.length - target.length + 1; i++) {
            for (int j = 0; j < target.length; j++) {
                if (array[i + j] != target[j]) {
                    continue outer;
                }
            }
            return i;
        }
        return -1;
    }

    /**
     * Returns the index of the last appearance of the value {@code target} in {@code array}.
     *
     * @param array  an array of {@code byte} values, possibly empty
     * @param target a primitive {@code byte} value
     * @return the greatest index {@code i} for which {@code array[i] == target}, or {@code -1} if no
     * such index exists.
     */
    public static int lastIndexOf(byte[] array, byte target) {
        return lastIndexOf(array, target, 0, array.length);
    }

    // TODO(kevinb): consider making this public
    private static int lastIndexOf(byte[] array, byte target, int start, int end) {
        for (int i = end - 1; i >= start; i--) {
            if (array[i] == target) {
                return i;
            }
        }
        return -1;
    }

    /**
     * Returns the values from each provided array combined into a single array. For example, {@code
     * concat(new byte[] {a, b}, new byte[] {}, new byte[] {c}} returns the array {@code {a, b, c}}.
     *
     * @param arrays zero or more {@code byte} arrays
     * @return a single array containing all the values from the source arrays, in order
     */
    public static byte[] concat(byte[]... arrays) {
        int length = 0;
        for (byte[] array : arrays) {
            length += array.length;
        }
        byte[] result = new byte[length];
        int pos = 0;
        for (byte[] array : arrays) {
            System.arraycopy(array, 0, result, pos, array.length);
            pos += array.length;
        }
        return result;
    }

    /**
     * Returns an array containing the same values as {@code array}, but guaranteed to be of a
     * specified minimum length. If {@code array} already has a length of at least {@code minLength},
     * it is returned directly. Otherwise, a new array of size {@code minLength + padding} is
     * returned, containing the values of {@code array}, and zeroes in the remaining places.
     *
     * @param array     the source array
     * @param minLength the minimum length the returned array must guarantee
     * @param padding   an extra amount to "grow" the array by if growth is necessary
     * @return an array containing the values of {@code array}, with guaranteed minimum length {@code
     * minLength}
     * @throws IllegalArgumentException if {@code minLength} or {@code padding} is negative
     */
    public static byte[] ensureCapacity(byte[] array, int minLength, int padding) {
        checkArgument(minLength >= 0, "Invalid minLength: %s", minLength);
        checkArgument(padding >= 0, "Invalid padding: %s", padding);
        return (array.length < minLength) ? Arrays.copyOf(array, minLength + padding) : array;
    }

    /**
     * Returns an array containing each value of {@code collection}, converted to a {@code byte} value
     * in the manner of {@link Number#byteValue}.
     *
     * <p>Elements are copied from the argument collection as if by {@code collection.toArray()}.
     * Calling this method is as thread-safe as calling that method.
     *
     * @param collection a collection of {@code Number} instances
     * @return an array containing the same values as {@code collection}, in the same order, converted
     * to primitives
     * @throws NullPointerException if {@code collection} or any of its elements is null
     * @since 1.0 (parameter was {@code Collection<Byte>} before 12.0)
     */
    public static byte[] toArray(Collection<? extends Number> collection) {
        if (collection instanceof ByteArrayAsList) {
            return ((ByteArrayAsList) collection).toByteArray();
        }

        Object[] boxedArray = collection.toArray();
        int len = boxedArray.length;
        byte[] array = new byte[len];
        for (int i = 0; i < len; i++) {
            // checkNotNull for GWT (do not optimize)
            array[i] = ((Number) checkNotNull(boxedArray[i])).byteValue();
        }
        return array;
    }

    /**
     * Returns a fixed-size list backed by the specified array, similar to {@link
     * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
     * set a value to {@code null} will result in a {@link NullPointerException}.
     *
     * <p>The returned list maintains the values, but not the identities, of {@code Byte} objects
     * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
     * the returned list is unspecified.
     *
     * @param backingArray the array to back the list
     * @return a list view of the array
     */
    public static List<Byte> asList(byte... backingArray) {
        if (backingArray.length == 0) {
            return Collections.emptyList();
        }
        return new ByteArrayAsList(backingArray);
    }

    private static class ByteArrayAsList extends AbstractList<Byte>
            implements RandomAccess, Serializable {
        final byte[] array;
        final int start;
        final int end;

        ByteArrayAsList(byte[] array) {
            this(array, 0, array.length);
        }

        ByteArrayAsList(byte[] array, int start, int end) {
            this.array = array;
            this.start = start;
            this.end = end;
        }

        @Override
        public int size() {
            return end - start;
        }

        @Override
        public boolean isEmpty() {
            return false;
        }

        @Override
        public Byte get(int index) {
            checkElementIndex(index, size());
            return array[start + index];
        }

        @Override
        public boolean contains(Object target) {
            // Overridden to prevent a ton of boxing
            return (target instanceof Byte) && Bytes.indexOf(array, (Byte) target, start, end) != -1;
        }

        @Override
        public int indexOf(Object target) {
            // Overridden to prevent a ton of boxing
            if (target instanceof Byte) {
                int i = Bytes.indexOf(array, (Byte) target, start, end);
                if (i >= 0) {
                    return i - start;
                }
            }
            return -1;
        }

        @Override
        public int lastIndexOf(Object target) {
            // Overridden to prevent a ton of boxing
            if (target instanceof Byte) {
                int i = Bytes.lastIndexOf(array, (Byte) target, start, end);
                if (i >= 0) {
                    return i - start;
                }
            }
            return -1;
        }

        @Override
        public Byte set(int index, Byte element) {
            checkElementIndex(index, size());
            byte oldValue = array[start + index];
            // checkNotNull for GWT (do not optimize)
            array[start + index] = checkNotNull(element);
            return oldValue;
        }

        @Override
        public List<Byte> subList(int fromIndex, int toIndex) {
            int size = size();
            checkPositionIndexes(fromIndex, toIndex, size);
            if (fromIndex == toIndex) {
                return Collections.emptyList();
            }
            return new ByteArrayAsList(array, start + fromIndex, start + toIndex);
        }

        @Override
        public boolean equals(Object object) {
            if (object == this) {
                return true;
            }
            if (object instanceof ByteArrayAsList) {
                ByteArrayAsList that = (ByteArrayAsList) object;
                int size = size();
                if (that.size() != size) {
                    return false;
                }
                for (int i = 0; i < size; i++) {
                    if (array[start + i] != that.array[that.start + i]) {
                        return false;
                    }
                }
                return true;
            }
            return super.equals(object);
        }

        @Override
        public int hashCode() {
            int result = 1;
            for (int i = start; i < end; i++) {
                result = 31 * result + Bytes.hashCode(array[i]);
            }
            return result;
        }

        @Override
        public String toString() {
            StringBuilder builder = new StringBuilder(size() * 5);
            builder.append('[').append(array[start]);
            for (int i = start + 1; i < end; i++) {
                builder.append(", ").append(array[i]);
            }
            return builder.append(']').toString();
        }

        byte[] toByteArray() {
            return Arrays.copyOfRange(array, start, end);
        }

        private static final long serialVersionUID = 0;
    }

    /**
     * Reverses the elements of {@code array}. This is equivalent to {@code
     * Collections.reverse(Bytes.asList(array))}, but is likely to be more efficient.
     *
     * @since 23.1
     */
    public static void reverse(byte[] array) {
        checkNotNull(array);
        reverse(array, 0, array.length);
    }

    /**
     * Reverses the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
     * exclusive. This is equivalent to {@code
     * Collections.reverse(Bytes.asList(array).subList(fromIndex, toIndex))}, but is likely to be more
     * efficient.
     *
     * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
     *                                   {@code toIndex > fromIndex}
     * @since 23.1
     */
    public static void reverse(byte[] array, int fromIndex, int toIndex) {
        checkNotNull(array);
        checkPositionIndexes(fromIndex, toIndex, array.length);
        for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--) {
            byte tmp = array[i];
            array[i] = array[j];
            array[j] = tmp;
        }
    }
}
